1. Field of the Invention
The present invention relates generally to optimizing the efficiency of a port injected internal combustion engine, and more particularly but not by way of limitation to the balancing of the fuel to air ratio in all combustion cylinders so that each cylinder reaches a peak exhaust gas temperature at a common total engine fuel flow rate.
2. Discussion
Manipulating the fuel to air ratio in an internal combustion engine is commonly done by those skilled in the art in order to achieve the engine's rated performance characteristics, such as power and fuel consumption. Generally, there is a ratio that produces a maximum exhaust gas temperature (hereinafter "EGT"), occurring at the stoichiometric balance point where just enough combustion air is available for complete combustion of the fuel. Operating the engine above this ratio, rich of peak EGT, is typically advantageous in achieving maximum power such as during acceleration of an automobile or take-off and climb of an airplane. Conversely, operating the engine below this ratio, lean of peak EGT, is typically advantageous in achieving fuel savings when maximum power is not needed. Operating in the lean of peak EGT range furthermore provides the advantage of reduced cylinder head temperatures.
Many engines in service today, however, are inherently incapable of realizing the benefits of operating in the lean of peak EGT range due to cylinder-to-cylinder variation in fuel to air ratios. The imbalance means that individual cylinders reach a peak EGT at different total engine fuel flow rates. This produces a condition whereby at any given total engine fuel flow rate the individual cylinders are producing different horsepower values. On the rich side of peak EGT this condition is usually insignificant because the corresponding horsepower curve is typically flat in that range. On the lean side of peak EGT, however, this condition is usually significant because the corresponding horsepower curve typically drops off steeply in that range.
It is well known that an engine with such an inherent imbalance will run rough when leaned because the variations in power produced by combustion are transferred by the pistons to the crankshaft. The net result is an unbalanced torque on the crankshaft which produces vibration and roughness in the engine. To prevent vibration and rough running, the engine must be operated in the rich ratio range where the horsepower curve is relatively flat, where cylinder to cylinder variations in the fuel to air ratio and corresponding EGTs have little effect on engine horsepower.
Others have suggested the cause of the inherent variation in fuel to air ratio among cylinders is due to an uneven distribution of combustion air to the engine cylinders. Although this is a possible cause in a few poorly designed air distribution systems, addressing the problem from the standpoint that an air pressure differential exists in many engines, such as those employing a runner-riser air induction system, has yielded limited results. What is obviously overlooked by this approach is that an uneven air distribution would create roughness and vibration at all ratios rich of peak. Those skilled in the art will recognize that the problematic conditions of engine roughness and vibration are primarily associated with operating the engine in the lean ratio range.
What the prior references fail to teach is that in addition to air flow unbalance there are other contributing factors, such as that of occult fuel transfer and of injector variation. Occult fuel transfer occurs as rich mixtures in the inlet port of upstream cylinders is sucked into the combustion airstream of downstream cylinders when the upstream cylinder inlet port is closed. Injector variation comes from the common-place manufacturing tolerance or out of spec condition of an injector or its associated distribution system.
What is lacking in the industry is an approach that provides a matrix of fuel injectors, that is, a matched injector size for each cylinder, to provide an engine that equalizes the fuel to air ratio in all cylinders such that all cylinders reach a peak EGT at a common total engine fuel flow rate. Such a method would compensate for the variation caused by inherent engine conditions of construction such as occult fuel transfer and unbalanced combustion air, as well as fuel injector variation.